BACKGROUND OF THE INVENTION
The selector switch mechanism of the invention finds utility in electric programmer units, and it will be described in such an environment. It will become apparent as the description proceeds, however, that the switch has general utility in selector switch circuits in which a movable contact is caused to contact successively a plurality of fixed contacts to cause different circuits selectively to be energized.
Such an electric programmer is described, for example, in U.S. Pat. 3,101,418, which issued Aug. 20, 1963, and which is assigned to the present assignee. The particular programmer unit described in the aforesaid patent is one in which a relatively simple electric programming unit is used to control automatically a number of electrically operated valves in a sprinkler system. The programmer described in the patent includes a controlled wafer-type selector switch which is effective to cause different valve circuits to be energized in a sequential manner and automatically on a day-by-day basis.
However, in order to avoid undue arcing at the contacts of the prior art wafer-type selector switch due to the inductive nature of the load, a relatively complex switching system is used in the unit described in the patent, and which assures that the wafer switch is first operated from one contact to the next, before a second switch actually causes current to pass through the wafer switch.
By use of the snap-acting wafer selector switch of the present invention, the need for the extraneous circuitry described in the patent is obviated, and the wafer switch itself may be used to perform the current switching function.
The invention provides, therefore, a snap-acting wafer-type switch mechanism which is effective to minimize contact burning, especially with inductive loads. The switching mechanism to be described includes a double-acting pawl which function as an escapement mechanism, first to release the switch armature and then to stop it after it has moved through a predetermined angular distance. Under the control of the double-acting pawl, the movable contact of the switch breaks with the previously engaged fixed contact with a snap action, and it moves half way through the angular distance to the next fixed contact. Then, the action of the double-acting pawl causes the switch armature again to be released and move the movable contact into electrical engagement with the next fixed contact, also with a snap action.
By the action described in the preceding paragraph, the switching mechanism of the invention assures that a circuit energized by a particular position of the armature of the switch, is deenergized before the next circuit is energized thereby. This prevents the two circuits being energized at the same time, which could result in excessive loading on the system. For example, when the switching mechanism of the invention is used in a sprinkler system, it permits one valve to be turned off before the next is turned on, so that full fluid pressure may be maintained at all times.
A feature of the improved wafer snap-acting switch of the present invention is that it is extremely simple from a mechanical standpoint. Moreover, the improved snap-acting wafer switch of the invention simplifies the mechanical components and associated electric circuit when, for example, the mechanism is incorporated into a programmer unit of the general type described in the aforesaid patent. Specifically, when the snap-acting wafer selector switch of the invention is incorporated into such a programmer unit, it vastly reduces the complexity and cost of the unit and also improves its performance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a rear view showing the improved switching mechanism of the present invention mounted on a panel and incorporated into a programmer;
FIG. 2 is a front view of the programmer unit of FIG. 1;
FIG. 3 is a side view of the unit taken essentially along the line 3-3 of FIG. 1;
FIG. 4 is a detailed section of certain components of the switching mechanism in an expanded condition; and
FIG. 5 is a circuit diagram of an appropriate programmer in which the snap-acting wafer switching mechanism of the invention may be incorporated .
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
As shown in FIGS. 1--3, for example, the switching mechanism of the invention and associated components may be mounted on a stationary support such as a panel 10. The mechanism includes a usual selector multicontact leaf switch 12 which is mounted on the stationary support 10 by means, for example, of a mounting bracket 14. The leaf switch 12 includes a plurality of fixed contacts 16 to which appropriate electrical connections, such as the connection 18, may be made, and it also includes a movable contact 20 which is mounted on a drive shaft 22. As the drive shaft 22 is rotated, the movable contact 20 is caused to move from one of the fixed contacts 16 to the next, so as to establish selective electric contact with the successive fixed contacts.
A ratchet wheel 24 is keyed to the drive shaft 22, and it is engaged by a double-acting pawl 26, the pawl being pivotally mounted on the stationary support 10 by means, for example, of a screw 28. The double-acting pawl 26 forms an escapement mechanism with the ratchet 24, and the action is such that when the pawl is set in the angular position shown in FIG. 1, rotation of the ratchet wheel 24 and of the movable contact 20 in the clockwise direction is prevented. A drive gear 30 is rotatably mounted on a bushing on the shaft 22 and, as shown in FIG. 4, for example, is coupled to the shaft by means of a coil spring 32, so that rotation of the drive gear 30 causes it to exert a resilient torque on the drive shaft 22 which, in turn, biases the ratchet wheel 24 and the movable contact 20 in the clockwise direction.
Now, when the pawl 26 is released by an engagement of a protruding portion 26a of the pawl, as will be described, it moves in a clockwise direction to release the ratchet wheel 24. The ratchet wheel then turns through a limited angular distance until its next sprocket engages the right-hand end of the pawl in FIG. 1. When that occurs, the movable contact 20 has moved half the distance from the fixed contact 16 previously engaged by it, and the next fixed contact 16. Then, when the pawl is returned in a counterclockwise direction to the position shown in FIG. 1, the ratchet wheel moves through a further angular distance, so that the movable contact 20 is caused to engage the next contact 16.
Therefore, each time the pawl 26 is actuated and released, the movable contact 20 moves with a snap action to break the previously engaged fixed contact 16, and to establish itself at a distance midway between that contact and the next. Then, when the pawl is returned to its original position, the movement is completed, and the movable contact engages the next fixed contact, also with a snap action. In this way, and as described above, it is assured that the energized circuit is first broken, before the next circuit is energized. Also, it will be appreciated, that each time the pawl 26a is actuated, the movable contact moves with a snap action due to the bias force exerted on it by the spring 32.
In order to actuate the pawl 26, a program wheel 50 is mounted on a bushing on the drive shaft 22 on the opposite side of the panel 10 from the components described above, and the drive gear 30 is also mounted on the bushing. The program wheel 50 turns with the drive gear 30. The program wheel includes a plurality of adjustable radial stops 52 which may be set to any desired angular position around the periphery of the program wheel 50. When any one of the stops 52 engages the projecting portion 26a of the pawl 26, the pawl is actuated as described above. As mentioned, the stops 52 may be manually set to any desired position around the program wheel 50, so that as the program wheel is rotated, the pawl is actuated at desired times.
The drive gear 30 is coupled to a further gear 60 which is mounted on an idler shaft 62 with a pinion 64. A clock motor 66 is mounted on the stationary support 10, and a pinion 68 on the drive shaft of the clock motor is coupled to a gear 70. The gear 70 is mounted on a shaft 72, together with a segmented gear 74, the latter gear being mounted on the opposite side of the panel 10 from the clock motor 66 and gear 70, as shown in FIG. 2.
The clock motor 66 may drive the gear 70 at a particular rate of, for example, one revolution per day, so that the segmented gear 74 rotates at the same rate. The segmented gear 74 may include segments 76 which are mounted on the segmented gear by means, for example, of screws 78. The segments 76 are of a particular arc length to cause a complete revolution of the drive gear 30 during the engagement of each segment with the pinion 64. As shown in FIG. 2, two segments 76 may be provided to cause the drive gear 30 to make two revolutions per day, one during some 6 -hour interval, and another at some other 6 -hour interval, as determined by the position of the segments. This causes successive solenoid valve control circuits to be turned on and off, for example, during each of the aforesaid 6-hour intervals.
As shown in FIG. 1, for example, a microswitch 80 may be mounted on the stationary support 10 to be operated each time the pawl 26 is actuated. This switch, for example, may be used to control a signal, or any other appropriate device to indicate each time a circuit is activated or deactivated by the control mechanism.
The mechanism described above may be incorporated into an electric circuit, such as shown in FIG. 5.
The electrical system includes, for example, a connector strip 82 which includes a first pair of terminals A and B which are connected to the usual 110-volt source. When so connected, a transformer 84 is energized, and it develops an appropriate voltage for the clock motor 66 across its secondary. The clock motor is in the primary circuit of the transformer, and it is energized whenever the 110-volts is applied to the terminals A, B, at the same time the primary winding of the transformer is energized. The secondary circuit of the transformer is energized by closing a switch 86, causing current to flow through a fuse 88.
When the clock motor is energized, the movable contact 20 of the snap-acting wafer switch is caused to move from one fixed contact to the other, as described above, providing selective connections between the common terminal C and switching terminals D, E, F, G, H and J on the terminal strip 82. The microswitch 80 is actuated each time the wafer switch 16 is operated, providing for a connection between, for example, the terminal A and a further terminal K. It will be appreciated that any signalling device connected across the terminals K and B will be energized by the 110-volt AC current whenever the switch 80 is operated.
The circuit of FIG. 5 is extremely simple in that all the electrical switching connections are performed by the selector switch itself, due to its snap-acting feature, so that additional switching circuitry is unnecessary. The switching mechanism itself is relatively simple and may be constructed at a relatively low cost. The clock motor could be placed in the secondary circuit in position to stop whenever the fuse 88 is blown. The position of the selector switch at that time will indicate which valve circuit cause the failure.